The present invention relates to a thin-disc piezoelectric actuating ultrasonic motor, wherein an AC voltage is inputted into a piezoelectric element consisting of a piezoelectric ceramic and metal back plate. The piezoelectric ceramic generates a pull or push effect due to the reverse piezoelectric effect and the metal back plate in the piezoelectric element is driven to vibrate. The generated mechanical wave propagates in radial or transverse directions. As the wave propagates, each screw forms a reflecting point. Due to the reflecting points from three peripheral screws, traveling waves of different directions are formed by the piezoelectric buzz piece at the outer edge of the metal back plate. One of the traveling waves is used to provide a torque to cause the rotor to rotate.
The currently used ultrasonic motor is primarily formed by a piezoelectric (PZT) ceramic 12 made of a zirconium-titanium-acid-lead material, as illustrated for example in FIG. 1. After a voltage is inputted into the piezoelectric ceramic 12, the piezoelectric ceramic 12 and the metal back plate 11 will be forced to generate a mechanical extension-contraction phenomenon. Energy is transferred in a wave form. The piezoelectric ceramic operates within an ultrasonic frequency having an amplitude of several micrometers which is controllable by input voltage. Therefore, it can be used as a driving device or a driving motor of a compact structure or system.
The aforesaid ultrasonic motor may generate an alternating extension-contraction function by AC power. By mechanical design, motions in specific directions are generated. The moving distance in each period is only several micrometers. Under the vibration of the ultrasonic frequency, a displacement of several centimeters per second is generated for driving precise devices (such as automatic focusing means of a camera, positioning devices for fine machining, etc.). Meanwhile, the ultrasonic motor has the features of small volume, light weight, low noise, low speed with a high torque, high retaining force, quick response, insensitivity to electromagnetic interference, and so forth. Different advantages may be emphasized in different products, such as lower speed, high torque, high retaining force, and low noise in products designed for use in silent places (such as hospitals); quick response in products requiring driving a X-Y platform, and insensitivity to electromagnetic waves in products for use in magnetic floating vehicles and biomedical technology.
The prior art ultrasonic motors or actuators are made of piezoelectric bulk material or piezoelectric stacking pieces, however, that have a high cost, so that the commercial ultrasonic motor has a high price.
Accordingly, the primary object of the present invention is to provide an ultrasonic motor including a piezoelectric element into which is inputted an AC voltage. The piezoelectric ceramic in the piezoelectric element generates a pull-push effect due to a reverse piezoelectric effect and a metal back plate in the piezoelectric element is driven to vibrate. The generated mechanical wave propagates or transfers along a radial or transverse path. As the wave propagates, each screw in the back plate can be formed as a reflecting point. Due to the reflecting points from three peripheral screws, traveling waves of different directions can be formed by the piezoelectric element at the outer edge. One of the traveling waves is used to provide a torque to drive a rotor to rotate.
Another object of the present invention is to provide a thin-disc piezoelectric actuating ultrasonic motor, that can be used in semiconductor equipment, medical instruments, hard disk drives and CD drives, and that has a low cost and high efficiency.
To achieve the above objects, the present invention provides a thin-disc piezoelectric actuating ultrasonic motor, wherein a main electrode is covered at the uppermost surface of a piezoelectric element or ceramic, and the lowest end of the piezoelectric element is adhered to a metal back plate. In operation, AC power is inputted between the main electrode and the metal back plate. The piezoelectric ceramic will extend or shrink due to the reverse piezoelectric effect. In contrast to a conventional xe2x80x9cspeakerxe2x80x9d, in which the metal back plate is deformed by the piezoelectric ceramic so as to vibrate air for emitting a sound, at a working frequency of between 50 and 20 kHz, in the present invention, the piezoelectric element is used as a driver operating at a frequency of over 30 kHz. The working principle is that the piezoelectric element is used to vibrate the periphery of the metal back plate for driving the rotor to rotate.
In the thin-disc piezoelectric actuating ultrasonic motor of the present invention, the piezoelectric element including the metal back plate is fixed to a rectangular piece by three asymmetric screws. Then one side of the fixed rectangular piece is fixed to another rectangular piece larger than the former one by a plurality of screws and a spring so that an elastic resilient structure is formed between the two rectangular pieces. Then an AC current is inputted into the piezoelectric element so that the piezoelectric ceramic will extend and contract due to the reverse piezoelectric effect of the ceramic and drive the metal back plate to vibrate. The mechanical waves are transferred along the radial and transverse directions. The outer edge of the piezoelectric element generates traveling waves along different directions. The traveling waves will provide a torque to drive the rotor to rotate.
The piezoelectric element forms a motor stator consisting of the above-mentioned two major elements: one is a piezoelectric ceramic and another is a metal back plate. The principle of either standing or traveling waves in a stator is that an AC voltage applied to the main electrode of the piezoelectric element causes the piezoelectric ceramic as the main actuating body of the stator to generate a reverse piezoelectric effect to vibrate the metal back plate. Therefore, wave energy is transferred to the stator. The oscillation of friction material on the stator causes the shaft of a rotor to be rotated along the wave traveling direction. The traveling wave is generated because a disc with a single frequency can be formed to provide multiple reflections of the specific frequency. The intersection of these reflecting waves will form wave motions at a specific section.